The present invention relates to a moving bed reactor, suitable for the catalytic treatment of hydrocarbons, such as catalytic desulphurization and demetallization of petroleum residues. The reactor is of the type which contains at least one tray as well as supporting means for one or more catalyst beds, means which are permeable to liquid and gas and impermeable to catalyst particles and in which said supporting means are attached to the wall of the reactor and are at least partly in the shape of a conical surface of a truncated cone.
More particularly, the invention relates to a moving catalyst bed reactor comprising a vertical cylindrical vessel having separate inlets for reactant and catalyst at the upper part of the vessel and catalyst bed supporting means in the shape of one or more downwardly converging conical surfaces the lower end thereof being connected to one or more vertical outlet channels having circumferential walls for the combined passage of catalyst and separation of reactor effluent, said circumferential walls being provided with a screen section for withdrawing the effluent from the catalyst, and separate outlet conduits for reactor effluent and catalyst downstream of said screen section.
Moving bed reactors of a design as identified above are known. Examples thereof have been described, e.g., in U.S. Pat. Nos. 3,883,312 and 3,966,420. According to the first U.S. specification both the used solid catalyst and the reactor effluent are removed from a moving bed reactor through the same withdrawal conduit. The reactor effluent exits the conduit through perforations in its wall. The catalyst descends past the perforations and is washed by an upward moving wash oil which leaves through the same perforations. An alternative solution for the separation of reactor effluent and catalyst and optionally wash fluid has been described in U.S. Pat. No. 3,966,420, the screen section being situated in the conical part of the supporting means and being of specific design consisting of bars of particular configuration and slit type sieve openings.
Both solutions have their advantages and disadvantages. Vertical screen surfaces have a rather small risk that catalyst fines may penetrate into the sieve openings, but usually have, owing to their construction, a smaller sieve area than a screen provided in conical supporting means.
More recently there is a tendency to carry out such processes on an ever increasing scale resulting in growing problems in the constructional design of the reactors when scaled up to such large capacities. One such problem is the circumstance that the catlyst bed area is growing therewith and that separation of reactor effluent from parts of the bed at distance from a screen area becomes more and more difficult.
An object of the present invention is to overcome such scaling-up difficulties. There is provided, according to the invention, a moving bed reactor of the type specified above, in which the vertical outlet channels are provided with further wall portions within said channels each bearing a screen section for withdrawal of reactor effluent from the catalyst.
The invention further resides in measures for the adequate design of the supporting surface with its associated screen section adapted to the requirements in scaling up reactors of the type concerned in which the following process and design conditions have to be taken into account.
As far as the flow of fluids and solids are concerned, the mass flow behavior of the solids should be maintained, while the spread in residence time should be kept as small as possible. Further the pressure drop over the catalyst bed supporting and passage internals is to be kept as low as possible and the liquid redistribution has to be possible over an optimal percentage of the reactor cross-sectional area. Screen loads have to be in the same order of magnitude throughout the reactor for reasons of preventing as much as possible fouling of the screens and pinning of the catalyst particles against the screens. And finally, forces and stresses on the reactor internals supporting and guiding the catalyst should be carefully calculated and checked.